Pump installation



Oct. 30, 1962 G. T. SHOOSMITH 3,060,858

PUMP INSTALLATION Filed June 7, 1960 5 Sheets-Sheet 1 y E B a 9MAttorneys Oct. 30, 1962 G. T. sHoosMlTH 3,060,858

PUMP INSTALLATION Filed June 7, 1960 5 Sheets-Sheet 2 Oct. 30, 1962 G.T. SHOOSMITH 3,060,358

PUMP INSTALLATION Filed June 7, 1960 3 Sheets-Sheet 3 VLF Inventor\bMrbM ilnited rates 3,660,358 PUD/E ENSTALLATIGN Guy Taite Shoosmith,Gangbridge House, St. Mary Bourne, England Filed June 7, 196i), Ser. No.34,580 Claims priority, application Great Britain Nov. 24, 1955 5Claims. (Cl. 1103-41) This invention relates to pumps and is in part acontinuation of the invention disclosed in application Serial No.623,892 filed on November 23, 1956, now abandoned. More specifically,the invention relates to pump installations comprising two or morevariable-capacity pumps arranged to share a common load.

The load imposed on many pump installations varies over a wide range.Thus, for example, an electricity generating station having two or morevariable-capacity pumps for supplying fuel oil to the boiler-housedemands a high output from the pumps during peak periods and a lowoutput during off-peak periods. Because the pumps are of variablecapacity, they are, of course, able to accommodate these changes ofload. It is, however, inefi'lcient to continue to operate both or allthe pumps during off-peak periods when, for example, one pump isperfectly able to cope with the limited demand.

The main object of the invention is to obviate the inefiicient operationdescribed above.

Another object of the invention is to provide a pump installationwherein the pumps are brought into and out of operation automatically inaccordance with load requirements.

A further object of the invention is to provide a pump installationwhich includes an hydraulic accumulator serving both to control thedelivery pressure of the pumps and to operate switches which bring thepumps into and out of operation as required.

According to the invention, the pumps of the installation areelectrically controlled so as to be brought individually into or out ofoperation in accordance with load requirements, the electrical controlcircuit comprising a limit switch mechanism for each pump which isautomatically controlled in accordance with the instant position of thecapacity-varying means of the pump. The arrangement is such that, whenthe capacity-varying means of the pump or pumps actually operatingreaches one of two positions, at least one of the limit switchmechanisms is operated automatically so as to bring in another pump ifthe load is increasing or cut out a pump if the load is decreasing.

Thus, for example, a power station pump installation in accordance withthe invention and comprising two pumps can be operated as follows.

In the normal way, one pump only is required for supplying all the fueloil necessary to meet, say, up to 60% of the maximum load. As the loadincreases, the capacity of the pump increases correspondingly until itis delivering about 80% of its maximum output. At this stage thecapacity-varying means of the pump reach a position where a memberattached to them operates a limit switch in an electrical circuit. Theoperation of the switch causes a prime mover drying the second pump tobe started up, with the result that the load is shared between the twopumps which are both delivering about 40% of their maximum output.

As the load continues to increase the two pumps continue to share itbetween them. If, however, the load begins to fall so that the two pumpsare delivering only 30% of their maximum output, the capacity-varyingmeans of the first pump reach a position where the member attached tothem operates the limit switch in the opposite sense so as to shut downthe prime mover driving the second pump. The output of the first pumpthen auto- 3,65%,858 Patented Oct. 30, 1962 matically increases to 60%of its maximum output as it takes over the duty of supplying all thefuel oil required.

The electrical control of the present invention can, of course, beapplied to any number of pumps so that two, three, four or more pumpscan be switched in or cut out in sequence as the load increases ordecreases. The invention is not, moreover, limited to any particulartype of variable-capacity pump.

In order that the invention may be thoroughly understood, two pumpinstallations in accordance with it will now be described with referenceto the accompanying drawings, in which:

FIGURE 1 illustrates the layout and electrical control circuit of one ofthe installations;

FIGURE 2 illustrates the layout and electrical control circuit of theother installations; and

FIGURE 3 is a part-sectional view through one of the pumps used in theinstallation of FIGURE 2.

The installation shown in FIGURE 1 comprises three variable-capacitypumps 10, 12 and 14 of the sliding vane type driven by separate electricmotors 16, 1S and 20. The delivery side of each pump is connected to adelivery line 21 which is common to all three pumps. Each pump isprovided with a pressure-sensitive device connected by individualpassages 15, 17 and 19 to the delivery side of the pump for varying thecapacity of the pump automatically according to load requirements. Thesepressure-sensitive devices are located in housings 22, 24 and 26provided on top of the pumping chambers and comprise an hydrauliccylinder and piston of essentially the same construction as the cylinder86 and the piston 84 shown in FIG URE 3. The upper portions of thesethree hydraulic cylinders are connected by three separate pipe-lines 46,48 and 50 to three separate hydraulic accumulators 23, 25 and 27 whichapply in hydraulic load to the upper surfaces of the pistons in thehousings 22, 24 and 26. However, the load applied by the threeaccumulators is not the same in all three hydraulic cylinders, for areason which will be mentioned later.

Connected to the piston of each pressure-sensitive device is aswitch-actuating rod 28, 30 and 32 having a pair of cross piecesarranged to switch on and off a limit switch 34, 36 and 38. The limitswitches are connected in electrical circuit to the electric motors 16,18 and 20 and to a selector switch 40 the position of which determineswhich motor is to be started up first.

It will thus be seen that the limit switches control the supply ofcurrent to the motors and that the switches are themselves controlled bythe rods 28, 30 and 32 which move vertically in accordance with thecapacity of the pump. The sequence in which the motors come into and outof operation follows that already outlined in the introductory part ofthe specification except that the maximum load is shared between threepumps instead of two. Thus, when the selector switch 40 is moved intothe position in which it is shown in FIGURE 1, the motor 16 driving thepump 10 is started up. As the load increases the limit switch 34 isactuated by the switch-actuating rod 28 so as to start up the motor 18driving the pump 12. A further increase in load causes theswitch-actuating rod 30 to operate the switch 36 with the result thatthe motor 20 driving the pump 14 is also energised. All three pumps arenow operating. i

As the load falls, the sequence in which the pumps 12 and 14 will be cutout depends on the setting of their respective accumulators 25 and 27.Assuming that the pressure exerted by each accumulator is greatest inthe accumulator 23 and lowest in the accumulator 27, then theswitch-actuating rod 32 will rise more rapidly than the rods 28 and 30and will actuate switch 38. This will not however have the effect ofshutting down the motor 16 because the circuit to this motor is in factcomplete irrespective of the position of the switch 38. A furtherdecrease in the load causes the switch-actuating rod 30 to operate theswitch 36 with the result that the motor is de-energised. A stillfurther decrease in the load then causes the rod 28 to operate theswitch 34, and this stops the motor 18. The sole remaining pump nowoperating, namely, the pump 10, continues to operate until the switch 40is turned to its oil position (not shown in the drawings).

There is no automatic connection between the selector switch 40 and thethree accumulators 23, and 27. In operation, the loading applied by theaccumulators is adjusted manually after a decision has been made as towhich pump will be started up first. Further, although the switch 38apparently has no function when the switch 40 is used to start up themotor 16, it will of course come into operation whenever the switch 40is used to start up the motor 18 or the motor 20. In these two cases,one or other of the switches 34 or 36 will be rendered unnecessaryinstead of the switch 38.

A modification of the installation shown in FIGURE 1 consists inomitting the switch 38 so that the switch 40 is used solely to bring themotor 16 of the pump 10 into and out of operation. Thus, the first pump10 is started up through the manually-controlled switch 40, and thesecond and third pumps 12 and 14 are brought in thereafter as the loadincreases by the actuation of limit switch mechanisms 34 and 36associated with the first and second pumps only. Preferably, the limitswitch mechanism 34 associated with the first pump 10 is arranged tobring in the second pump when the first pump 10 is working at about 90%capacity, and the limit switch mechanism 36 associated with the secondpump brings in the third pump 14 when :the second pump 12 likewisereaches its 90% flow position. i

As already stated above, the three hydraulic accumulators 23, 25 and 27apply three diiferent pressures to the pressure-sensitive devices 22, 24and 26. For example, the hydraulic accumulator 23 applies a pressure ofabout 155 p.s.i. to :the device 22, while the two other accumulators 25and 27 apply pressures of 150 p.s.i. and 145 p.s.i. respectively to thedevices 24 and 26. This means that, with all three pumps running, adecrease in load causes the flow capacity of the third pump 14 to dropfirst. A further decrease in load results in a reduction of the capacityof the second pump 12, and the limit switch 'inechanism 36 associatedwith the second pump cuts out the third pump 14 directly the capacity ofthe second pump 12 has fallen to about 80%. Eventually, as the loadcontinues to decrease, the capacity of the first pump 10 will drop to80%, and the limit switch mechanism 34 associated with it will then cutout the second pump 12. The first pump 10 continues to operate until itis stopped by the manually-actuated switch 40 controlling the pump.

The variable-capacity pumps shown in the drawings are capable of runningat zero capacity. However, prolonged running of such pumps with no flowtaking place through them can cause over-heating and subsequentcarbonisation of the oil or other liquid being handled by the pumps. Toovercome this possibility, the capacity varying means of each pump areso arranged that the capacity of the pump cannot fall below 3%, forexample, by providing stops 90 (see FIGURE 3) within the pump casingwhich limit movement of the cage 80. This ensures that there is alwayssome flow of liquid through the pump while it is running. When the firstpump 10 only is operating and no liquid is being drawn from theinstallation at all, the flow of liquid is allowed for in theinstallation by providing a bleed-line 92 regulated by a valve 94 andleading from the common delivery main back to the source of supply onthe suction side of the pumps.

The suction side of each pump is provided with a non- .retur-n valve 96(see FIGURE 1) to ensure satisfactory operation of the installation, andit is also advisable for 75 the manually-actuated switch 40 controllingthe first pump 10 to be so designed that, when the switch is actuated toshut down the first pump, the circuits containing the limit switches 34and 36 are also broken to prevent unintentional starting-up of thesecond and third pumps.

The pump installation illustrated in FIGURE 2 is basically the same asthat shown in FIGURE 1, the same reference numerals being used for likeparts, and the common delivery line to which the pumps are connectedbeing shown at 42. However, in this installation the limit switchmechanisms are not operated by switch-actuating devices mounted on thepumps; instead they are actuated by a part of an hydraulic accumulator44 which is connected by three pipe-lines 46, 48 and 50 to the hydrauliccylinder of each pump. The hydraulic accumulator serves to apply acommon adjustable constant load to the piston n each hydraulic cylinder,the piston being, of course, part of the capacity-varying means of thepump.

The limit switch mechanisms are shown at 52, '54, 56, 58, 60 and 62 inFIGURE 2, the part of the hydraulic accumulator 44 which actuates themcomprising an abut ment 64. This abutment moves up and down with theweighted upper part 66 of the accumulator in response to up and downmovements of the capacity-varying means in the pumps. FIGURE 3 shows oneof the pumps in greater detail. The pumps each have an inlet 68 and anoutlet 70, and comprise a slotted rotor shaft 72 having sliding vanes 74which bear at their ends on surfaces formed on the rotor proper 76. Therotor 76 rotates within a sleeve 78 carried in a cage 80 which can bemoved up and down to vary the eccentricity of the shaft 72 relatively tothe rotor 76, and, therefore, the capacity of the pump. The means forvarying the capacity of the pump comprise a rod 82 connected to the cage80 at one end and to a piston 84 at the other end, the piston 84 beingarranged for sliding movement in a cylinder 86. The upper part of thecylinder is connected to the hydraulic accumulator 44 while the lowerpart is connected by a pipe-line 15 to the delivery side of the pump,this arrangement ensuring that the pump delivers at substantiallyconstant pressure.

From a consideration of FIGURE 3, it will be seen that the position ofthe'piston 84 in the cylinder 86 will vary in accordance with the loadon the pump. This is true of all three pumps in the installation.Accordingly, the position of the movable part 66 of the accumulator willalso vary in accordance with the total load on the pumps.

The operation of the installation shown in FIGURE 2 is as follows:

When the three pumps shown in FIGURE 2 are running full out to meet fullload conditions, the accumulator 66 will be at the bottom of its traveland switches 54, 60 and 62 will all be shut so as to keep all threepumps running. If now the load on the installation gradually decreases,the fluid pressure in the common delivery pipe will tend to rise. Thisin turn reduces the stroke or capacity of all three pumps sothat fluidis forced back into the accumulator through the pipes 46, 48 and 50. Theaccumulator therefore starts to rise and first of all opens switch 58 soas to cut out one of the pumps, then opens switch 56 so as to cut outthe second pinnp, and finally opens switch 52 so as to cut out the thirdpump. The accumulator is now in the position which it adopts for no loadoperation.

Directly a new load demand on the installation arises, the fluidpressure in the common delivery pipe will drop which allows theaccumulator to return fluid back to the pumps throughthepipes 46, 48 and50. In so doing the accumulator begins to drop and first closes switch54 so as to bring in pump 10, then closes switch 60 so as to bring inpump 12, and finally closes switch 62 so as to bring in pump 14. Theinstallation is now working on high load or' full load operation.

Thus, the switches 52, 54, '56, 58, 60 and 62 have the followingfunctions:

Operation of switch 52 cuts out pump Operation of switch 54 brings inpump 10 Operation of switch 56 cuts out pump 12 Operation of switch 58cuts out pump 14 Operation of switch 60 brings in pump 12 Operation ofswitch 62 brings in pump 14 It therefore follows that, in the positionof the accumulator abutment 64 shown in FIGURE 2, pump 10 only isoperating. As the load increases, the abutment 64 will move downwardsuntil it actuates switch 60 so as to bring in pump 12. If the loadincreases still further, the abutment will actuate switch 62 so as tobring in pump 14. A decrease in the load will result in the abutment 64moving upwards so as to operate switches 58, 56 and 52 successively andthus cut out in turn pumps 14, 12 and .10 respectively.

I claim:

1. A pump installation comprising a first variable-capacity rotary pumpand a second variable-capacity rotary pump connected respectively tofirst constant-speed driving means and to second constant-speed drivingmeans for driving said pumps independently of each other, a rotorsurrounding a slotted rotor shaft in each of said pumps, said slottedrotor shafts in said two pumps carrying sliding vanes arranged to bearon surfaces formed on said rotors, said rotors being supported insliding blocks for relative movement to said rotor shafts so as to varythe eccentricity of said rotors relatively to said rotor shafts, fluiddelivery outlets from said pumps leading into a single delivery passagewhereby said pumps share a common load, electrical control meansoperatively connected to said first driving means and to said seconddriving means for bringing said pumps individually into and out ofoperation by the actuation of at least one limit switch mechanismforming part of said electrical control means, switch-actuating meansarranged to actuate said limit switch mechanism and operativelyconnected to said sliding block of said first pump so as to move inaccordance with movements thereof whereby said limit switch mechanism isoperated when said sliding block of said first pump reaches one of twopositions, pressure-sensitive power means on each pump connected by apassage to said fluid delivery outlet thereof and adapted to move saidsliding block in accordance with variations in the pressure in saidsingle delivery passage, said electrical control means including anelectrical connection between said limit switch mechanism and saidsecond driving means to ensure starting up of said second driving meansas the pressure in said single delivery passage decreases and shuttingdown of said second driving means as the said pressure increases.

2. The pump installation as claimed in claim 1, wherein said electricalcontrol means also including a manuallyactuated switch for maintainingsaid first driving means under manual control.

3. A pump installation as claimed in claim 1, wherein a single hydraulicaccumulator is connected by pipelines to said power means on each ofsaid pumps whereby a movable part on said accumulator is moved inaccordance with movements of said sliding blocks in said pumps, saidmovable part being arranged .to actuate said limit switch mechanism.

4. A pump installation as claimed in claim 1, wherein hydraulicaccumulator means are provided for applying hydraulic loads to saidpower means on each of said pumps through separate pipeline connectionsbetween said accumulator means and said power means.

5. A pump installation as claimed in claim 1, wherein at least twoseparate hydraulic accumulators are provided for applying diiierenthydraulic loads to said power means on each of said pumps throughseparate pipeline connections between said hydraulic accumulators andsaid power means.

References Cited in the file of this patent UNITED STATES PATENTS1,807,328 Warren May 26, 1931 1,972,812 Woolley Sept. 4, 1934 2,029,765Durdin Feb. 4, 1936 2,366,388 Crosby Jan. 2, 1945 2,526,646 Ericson Oct.24, 1950 2,682,227 Burris June 29, 1954 2,741,986 Smith Apr. 17, 19562,791,179 Dorer May 7, 1957 2,813,231 Hyde Nov. .12, 1957 FOREIGNPATENTS 287,785 Germany Feb. 14, 1914 338,580 Great Britain Nov. 24,1930 430,701 France Oct. 23, 1911 669,694 Germany Aug. 2, 1936 813,336France May 31, 1937

